It is well known that the probability of surviving a heart attack depends on the speed with which appropriate medical care is provided. One of the most common and life-threatening consequences of a heart attack is the development of a cardiac arrhythmia such as a ventricular fibrillation, in which the heart is unable to pump a sufficient volume of blood. When such an arrhythmia occurs, serious brain damage and death will invariably result unless a normal heart rhythm can be restored within a few minutes.
The most effective treatment for ventricular fibrillation is the application of a strong electric shock to the victim. The electric shock frequently terminates the chaotic activity characteristic of arrhythmias, and restores the normal pumping action of the heart. Defibrillators for producing and delivering such shocks have been known and successfully used for many years.
An important feature that exists in many portable as well as nonportable defibrillators is the ability to record data surrounding a defibrillation event for later analysis. Most emergency medical organizations have standard protocols that describe how first responders and emergency medical care providers should treat patients during medical emergencies, such as cardiorespiratory emergencies. To assess the effectiveness of these protocols, information about the patient condition and the procedures performed must be collected for post-event review. Event summaries may include patient information, recorded electrocardiograms (ECGs), results of patient assessments, and times of medication and therapy delivery. The data may also include time-coded data corresponding to functions implemented by a defibrillator user, and voice or other data recorded at the site of the emergency. The event data may further include a time index of when the defibrillation pulses were applied to the patient, the energy of each pulse, patient impedance data, and other patient and system events necessary to reconstruct the defibrillation therapy. All event data are preferably associated with time stamps so that an accurate timeline can later be reconstructed for analysis.
A typical method of accessing the stored data is to later download it through a dedicated data port located on the defibrillator. To download the data using known methods, a communication cable is connected between the dedicated data port on the defibrillator and a communication port on a computer. Data surrounding the defibrillation event is then downloaded to the computer where it may be stored for later analysis.
Accurate time stamps on the recorded event data are desirable in order to ensure that event reconstruction and analysis are meaningful. Inaccurate time stamps can result from the internal clock of the defibrillator being out of synchronization with a reference time base maintained by the emergency medical system. Event data that is recorded by a defibrillator having an internal clock out of synchronization with the reference clock that is later used for event reconstruction can yield incongruous results. An example of an incongruous result is a time stamp indicating that the defibrillator applied a defibrillation shock to a patient at an emergency scene at a time after the patient's arrival at the emergency room was logged according to the reference clock.
The probability that incongruous results will occur increases as the number of first responders and emergency care providers continues to grow. The worsening of the time-reporting aspect of a medical emergency may result from the failure of a care provider to use a reference clock, the care provider's use of unsynchronized clocks, or haphazard data logging techniques. Moreover, local protocols may not be in place to ensure clock synchronization to a reference time standard. As a result, incongruous time stamps are often placed on event data recorded by different organizations, precluding meaningful emergency event reconstruction and analysis.